It is common knowledge that foamed polymers are susceptible to various forms of degradation, for example, degradation due to the effect of oxygen and heat acting deleteriously on the polymer chains.
In its homopolymeric form, polystyrene, which contains no reinforcing polymeric materials such as rubber, is termed crystal polystyrene. This material is normally a transparent colorless resin used for making injection molded articles and films. This material is also used in the manufacture of expanded thermoplastic polystyrene foams by the use of a blowing agent such as a hydrocarbon or a chloro-fluorocarbon compound, under conditions causing vaporization of the blowing agent during extrusion of the polymer. During production of thermoformed articles from extruded foam polystyrene sheet, thermal oxidative degradation of polystyrene can occur to an extent having an adverse effect on the physical properties of the thermoformed articles.